fix(GraphQL): fix internal Aliases name generation (#7009)

This PR modifies how the internal graph aliases are generated in case of multiple aliases of same field in the query.
For the given graphql query:
```
query {
      queryAuthor {
        name
        p1: posts(filter: {isPublished: true}){
          title
          text
        }
        p2: posts(filter: {isPublished: true}){
          title
          text
        }
      }
    }
```
earlier it was rewritten into:
```
query {
      queryAuthor(func: type(Author)) {
        name : Author.name
        posts : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        posts1 : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        dgraph.uid : uid
      }
    }
```
Now it is changed to:
```
query {
      queryAuthor(func: type(Author)) {
        name : Author.name
        posts : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        posts.1 : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        dgraph.uid : uid
      }
    }
```

(cherry picked from commit 953f656)

graphql/resolve/query_rewriter.go

@@ -1170,14 +1170,14 @@ func buildAggregateFields(
 
 // Generate Unique Dgraph Alias for the field based on number of time it has been
 // seen till now in the given query at current level. If it is seen first time then simply returns the field's DgraphAlias,
-// and if  it is seen let's say 3rd time  then return "fieldAlias3" where "fieldAlias"
+// and if  it is seen let's say 3rd time  then return "fieldAlias.3" where "fieldAlias"
 // is the  DgraphAlias of the field.
 func generateUniqueDgraphAlias(f schema.Field, fieldSeenCount map[string]int) string {
 	alias := f.DgraphAlias()
 	if fieldSeenCount[alias] == 0 {
 		return alias
 	}
-	return alias + strconv.Itoa(fieldSeenCount[alias])
+	return alias + "." + strconv.Itoa(fieldSeenCount[alias])
 }
 
 // TODO(GRAPHQL-874), Optimise Query rewriting in case of multiple alias with same filter.

graphql/resolve/query_test.yaml

@@ -2584,7 +2584,7 @@
           text : Post.text
           dgraph.uid : uid
         }
-        posts1 : Author.posts @filter(eq(Post.isPublished, false)) {
+        posts.1 : Author.posts @filter(eq(Post.isPublished, false)) {
           title : Post.title
           text : Post.text
           dgraph.uid : uid
@@ -2618,7 +2618,7 @@
           text : Post.text
           dgraph.uid : uid
         }
-        posts1 : Author.posts @filter(eq(Post.isPublished, true)) {
+        posts.1 : Author.posts @filter(eq(Post.isPublished, true)) {
           title : Post.title
           text : Post.text
           dgraph.uid : uid
@@ -2674,8 +2674,8 @@
     query {
       queryAuthor(func: type(Author)) {
         count_postsAggregate : count(Author.posts)
-        count_postsAggregate1 : count(Author.posts) @filter(gt(Post.tags, "abc"))
-        count_postsAggregate2 : count(Author.posts) @filter(le(Post.tags, "xyz"))
+        count_postsAggregate.1 : count(Author.posts) @filter(gt(Post.tags, "abc"))
+        count_postsAggregate.2 : count(Author.posts) @filter(le(Post.tags, "xyz"))
         dgraph.uid : uid
       }
     }